The present invention relates to a guide unit in which a track shaft and a sliding member are engaged with each other such that they are capable of relatively reciprocating via rolling bodies such as balls or rollers of ball bearing, ball bushing, ball screw, ball spline, roller bearing or the like for linear sliding and curved sliding, and more particularly to a dust preventing structure of a guide unit for removing foreign matter adhering to the surface of the track shaft and applying lubricating performance between the track shaft and sliding member.
This kind of the guide units are used in various fields requiring a linear motion, rotary motion, a curved motion and the like and their use conditions are diversified. For example, a guide unit of linear sliding type ball bearing for use in semiconductor manufacturing apparatus is used under a very clean environment, a guide unit of machine tool is used under an environment in which coolant is used and further, a guide unit of timber processing unit is used under a condition in which dust, dirt, wooden pieces, cutting powder and the like falls thereon.
In such a guide unit, if foreign matter such as coolant and dust invades into a gap between the track shaft and sliding member, the coolant repels lubricant or foreign matter absorbs lubricant, so that lubricity between the track shaft and sliding member drops considerably. As a result, rolling bodies such as balls or rollers bearing a load between the track shaft and sliding member or the track shaft in which the rolling bodies roll and the rolling groove in the sliding member side are worn abnormally thereby the service life of the unit dropping remarkably.
Thus, in a conventional linear sliding motion ball bearing comprising a track rail (track shaft) in which a ball rolling groove is formed in the length direction thereof and a sliding base (sliding member) in which a ball infinite circulation path constituted of a load rolling groove opposing the ball rolling groove in the aforementioned track rail via a plurality of balls, a direction changing path disposed at beginning and terminal ends of the load rolling groove and a ball return path connecting these direction changing paths is formed, sealing members made of rubber or the like are attached to both ends in the traveling direction of the sliding base so that they are in firm contact with the track rail, thereby removing coolant, dust and the like adhering to the surface of the track rail in the accordance the movement of the sliding base to prevent them from invading into the interior of the sliding base.
In case where, in this kind of the guide unit, foreign matter such as welding spatter or the like adheres to the track rail, if the aforementioned sealing member makes contact with the spatter, it may be caught thereby and damaged. To avoid such an inconvenience, according to another known structure of the guide unit, a scraper member made of metal or the like is attached outside of the sealing member of the sliding base with a slight gap with respect to the track rail, so that the foreign matter such as welding spatter adhering to the track rail is scraped out by this scraper member before the sealing member comes into contact with the spatter.
Because this kind of the sealing member keeps a firm contact with the track shaft (track rail in the previous example), lubricant such as lubricating oil and grease supplied inside the sliding member (sliding base in the previous example) and adhering to the surface of the track shaft is wiped off by a sealing member at the rear side of the sliding member in the advancement direction so as to prevent the lubricant from leaking out of the sliding member (lubricant leakage preventing function).
This lubricant leakage preventing function of this sealing member exerts an effect of using lubricant supplied inside the sliding member effectively. If an attention is paid to a sealing member located at the front side in the advancement direction when the sliding member reciprocates, it comes that this sealing member moves with a firm contact with the surface of the track shaft after lubricant is wiped off, so that friction resistance increases as compared to the sealing member located at the rear side in the advancement direction. As a result, a smooth reciprocation of the sliding member is prevented and if a reciprocating stroke is extremely long, the sealing member located at the front side in the advancement direction may be damaged by a friction caused between the sealing member and the track shaft or the service life of the sealing member may be shortened extremely.
This problem occurs like a case in which a scraper member made of metal, plastics or the like is used with the sealing member. Although the scraper member is capable of removing a large foreign matter such as spatter, because it cannot be mounted in a firm contact with the surface of the track shaft, it is not capable of removing small dust or dirt and when the sliding member reciprocates, the sealing member located at the front side in the advancement direction comes into contact with the small dust or dirt, so that friction resistance increases thereby the service life being reduced.
If the guide unit is used under a condition in which use of coolant is required or under an environment in which dust, dirt, wooden pieces, cutting powder or the like falls, this problem is very conceivable because after the sealing member wipes off, a slight amount of lubricant remaining on the surface of the track shaft is washed off by those foreign matters or absorbed. This problem needs to be solved to accelerate maintenance free about lubricant in a guide unit for use under such a severe condition.
Accordingly, the inventor of the present invention considered a solution of this problem earnestly. As a result, the inventor of the present invention has completed a dust preventing structure of a guide unit capable of achieving a smooth reciprocation with less friction resistance of the sliding member with respect to the track shaft, preventing foreign matter from invading inside of the sliding member even if use of the sealing member is omitted if it is not used under a severe environment and further maintaining a smooth reciprocation of the sliding member with respect to the track shaft in a long period even under a severe condition in which use of coolant is required or dust, dirt, wooden pieces, cutting powder or the like falls on the guide unit, by using the sealing member at the same time.
Therefore, an object of the present invention is to provide a dust preventing structure of a guide unit capable of achieving a smooth reciprocation of the sliding member with respect to the track shaft with less friction resistance.
Further, another object of the present invention is to provide a dust preventing structure of a guide unit capable of maintaining a smooth reciprocation of the sliding member with respect to the track shaft in a long period even under a severe condition in which use of coolant is required or dust, dirt, wooden pieces, cutting powder or the like falls on the guide unit.
To achieve the above object, according to an aspect of the invention, there is provided a dust preventing structure of a guide unit comprising a track shaft and a sliding member engaging the track shaft via a plurality of rolling bodies so that it is capable of reciprocating in a length direction thereof, wherein elastic members in firm contact with the track shaft are overlaid in the length direction of the track shaft.
Further, according to another aspect of the invention, there is provided a dust preventing structure of a guide unit comprising a track shaft and a sliding member engaging the track shaft via a plurality of rolling bodies so that it is capable of reciprocating in a length direction thereof, the dust preventing structure further comprising a lubricant pocket forming member having a concave groove portion made of elastic material for forming a lubricant pocket filled with lubricant together with the surface of the track shaft.
Then, according to a preferred embodiment of the present invention, there is provided a dust preventing structure of a guide unit comprising a track shaft and a sliding member engaging the track shaft via a plurality of rolling bodies so that it is capable of reciprocating in a length direction thereof, the dust preventing structure further comprising a lubricant pocket forming member made of elastic material, including a lubricant supplying portion which is in firm contact with the track shaft holding lubricant for supplying lubricant to the surface of the track shaft upon use and a concave groove portion for forming a lubricant pocket filled with lubricant together with the surface of the track shaft.
According to the present invention, basically, the aforementioned lubricant pocket forming member is made of elastic material and includes the lubricant supplying portion which is in firm contact with the track shaft holding lubricant for supplying lubricant to the surface of the track shaft upon use and the concave groove portion for forming the lubricant pocket to be filled with lubricant together with the surface of the track shaft. If the lubricant supplying portion made of elastic material is capable of coating the surface of the track shaft with lubricant loaded in the lubricant pocket, with some extent of stiffness and holding a sufficient amount of lubricant, this lubricant pocket forming member can be formed with only the elastic material for forming the lubricant supplying portion. In this case, the lubricant pocket forming member may be formed with a single component member having a single or plural stripes of the concave groove portions or may be formed with plural component members when a single or plural stripes of the concave groove portions are formed when they are combined.
However, if as lubricant to be loaded in the lubricant pocket, for example, grease or solid lubricant is used, coating resistance which is generated when each of these lubricants is applied to the surface of the track shaft increases, so that an elastic material capable of holding a sufficient amount of lubricant considering a durable period of the dust preventing structure of the present invention may not be capable of bearing this coating resistance. Preferably, this lubricant pocket forming member comprises a plurality of elastic members constituting the lubricant supplying portion holding lubricant and spacer members which are made of stiff material and sandwiched between the plural elastic members so as to form a single or plural stripes of concave groove portions with the elastic members.
The size and quantity of the concave groove portion formed in the lubricant pocket forming member are not restricted to any particular ones, requirement for the lubricant pocket is satisfied if at least one stripe of the concave groove portion is formed and a sufficient amount of lubricant can be loaded in the lubricant pocket formed by this concave groove portion and the surface of the track shaft considering the durable period of the dust preventing structure of the present invention. Further, this concave groove portion needs to extend over an entire range in the direction of an outside periphery in which the sliding member covers the track shaft, so that lubricant can be applied to a substantially entire range in which the sliding member covers the track shaft.
The elastic material for forming at least the lubricant supplying portion of the aforementioned lubricant pocket forming member is continuously foamed body such as a continuously foamed polyurethanefoam and sintered resin or fiber entangled body such as wool felt, having physical properties including a tensile strength of 30-50 kg/cm3, degree of elongation of 300-500%, and impact resilience of 30-60% and made to absorb and hold lubricant after it is formed to a predetermined shape. If the elastic member is formed of rubber or synthetic resin, lubricant is mixed with the rubber or synthetic resin preliminarily and formed to a predetermined shape. Alternatively, lubricant is mixed with monomer at a stage where monomer is polymerized so as to produce rubber or synthetic resin and an obtained rubber or synthetic resin containing lubricant is formed to a predetermined shape. Meanwhile, in case where the aforementioned polyurethanefoam is soaked with lubricant, preferably, the lubricant should be 30-50 weight % in terms of weight ratio.
The lubricant to be loaded in the aforementioned lubricant pocket may be in any condition of fluid, solid or gelatinous as long as it has a lubricating performance and can be loaded in the lubricant pocket. Although fluid lubricant having a relatively low viscosity can be used, the lubricant is preferred to have a high viscosity of more than 200 cst because such a lubricant is not likely to leak out of the lubricant pocket or in the form of paste, solid state or gelatinous state. More specifically, grease, high viscosity lubricant, solid lubricant, or gelatinous or solid state wax, or the like can be mentioned. Particularly, grease is preferred because it forms a lubricant coating film having an excellent durability (that is, lubricant coating film having an excellent anti-coolant performance) under a condition in which coolant is used.
In case where the lubricant pocket forming member is composed of a plurality of the elastic members and spacer members, the same elastic members as those for forming the lubricant supplying portion can be used and the spacer members may be formed of metallic plate or synthetic resin plate. Preferably, the spacer member is made of a metallic plate such as stainless plate because its mechanical characteristic value is excellent.
Further, according to the present invention, it is preferable to provide a scraper member which holds the aforementioned lubricant pocket forming member by sandwiching it between the scraper member and the sliding member. This scraper member needs to have such a strength that it is never deformed or damaged when it removes foreign matter adhering to the surface of the track shaft such as welding spatter and it is attached to the sliding member with a slight gap with respect to the surface of the track shaft, for example, a gap of 0.05-0.3 mm.
Preferably, this scraper member is formed into a shape capable of covering substantially entirely the lubricant pocket forming member with both ends of the sliding member in the advancement direction and the surface of the track shaft so as to protect the lubricant pocket forming member having the lubricant supplying portion formed of the elastic material from an impact given from outside, and foreign matter such as coolant, dust, cutting powder and the like.
The dust preventing structure of the present invention having the lubricant pocket forming member is accommodated in various guide units in diversified patterns.
The guide unit to which the dust preventing structure of the present invention is applied basically comprises the track shaft and the sliding member engaging this track shaft via a plurality of the rolling bodies such that it is capable of reciprocating in the length direction thereof and this dust preventing structure is mounted on each of both ends of the sliding member of the guide unit in the advancement direction thereof.
The guide unit to which the dust preventing structure of the present invention is applicable includes not only the linear sliding type ball bearing comprising the track rail (track shaft) having the ball rolling grooves and the sliding base (sliding member) engaging the track rail via a plurality of balls such that it is capable of reciprocating in the length direction thereof and having an infinite circulation path for the balls, but also a ball screw comprising a screw shaft (track shaft) having a spiral ball rolling groove and a nut member (sliding member) engaging the screw shaft via a plurality of balls such that it is capable of reciprocating and having an infinite circulation path for the balls, curved sliding type ball bearing, ball bushing, ball spline and roller bearings for linear sliding and curved sliding and the like.
The sliding member of the guide unit to which the dust preventing structure of the present invention is mounted may be or may not be provided with a sealing member for sealing between inside and outside of this sliding member at both end portions in the advancement direction and this is selectable depending on use condition of the guide unit.
Although the lubricant supplying member is disposed as required between the sliding member and sealing member, the dust preventing structure of the present invention may be or may not be provided with that lubricant supplying member. This is also selectable depending on use condition of the guide unit.
Regardless of it that the sliding member of the guide unit is provided with the sealing member and the lubricant supplying member, the dust preventing structure of the present invention is disposed most outside of both ends in the advancement direction of the sliding member and the lubricant supplying portion of the lubricant pocket forming member slides in firm contact with the surface of the track shaft to remove relatively small foreign matter and further lubricant loaded in the lubricant pocket formed by the lubricant pocket forming member is applied to the surface of the track shaft.
In case where the aforementioned scraper member is disposed outside of the lubricant pocket forming member, this scraper member exerts a function of scraping out a relatively large foreign matter adhering to the surface of the track shaft ahead of the lubricant pocket forming member.
Thus, according to the dust preventing structure of the present invention, it is used with, for example, the sealing member and lubricant supplying member, and even if the guide unit is used under a severe condition in which use of coolant is required or dust, dirt, wooden pieces, cutting powder or the like falls thereon, it can remove foreign matter on the surface of the track shaft securely and apply lubricant to the surface of the track shaft to form lubricant coating film before the sealing member comes into contact with the surface of the track shaft or lubricant is supplied to the surface of the track shaft by the lubricant supplying member. As a result, such an event that the sealing member is damaged or supplied lubricant is repelled by foreign matter remaining on the surface of the track shaft, particularly coolant so that it is not supplied uniformly to the entire surface of the track shaft never occurs, so that a smooth reciprocation of the sliding member with respect to the track shaft can be maintained in a long period.
Of course, if the guide unit is not used under such a severe condition, the dust preventing structure of the present invention may be mounted directly on both ends in the advancement direction of the sliding member without using the sealing member or lubricant supplying member, thereby achieving two roles of removing foreign matter from the surface of the track shaft and supplying lubricant to the surface of the track shaft at the same time.
According to the present invention, it is possible to provide a dust preventing structure of a guide unit capable of not only achieving a smooth reciprocation of the sliding member with respect to the track shaft with less friction resistance but also maintaining a smooth reciprocation of the sliding member with respect to the track shaft in a long period even under a severe condition in which use of coolant is required or dust, dirt, wooden pieces, cutting powder falls on the guide unit.